So his death Saturday on his 75th birthday, at Rush University Medical Center’s Horizon Hospice on South Paulina Avenue, left many Chicagoans wondering how the void he has left could possibly be filled. He died of “a rare heart disease,” cardiac amyloidosis, said Marilyn Damon, his wife.

“I truly cannot imagine Chicago entertainment without Jimmy Damon, because he personified Chicago entertainment,” said Denise McGowan Tracy, an impresario who was mentored by the singer since the early 1980s.

“When we started ‘Monday Night Live’ at Petterino’s,” added Tracy, referring to the weekly cabaret sessions at the Loop restaurant, “he came down (wearing) a T-shirt that said: ‘Monday Night Live at the Playboy Club.’

“And I said, ‘Oh my God, we stole your idea.’

“But he said: ‘I’m thrilled.’”

As usual, Damon had been there first. Indeed, he championed jazz-swing standards in uncounted Chicago venues since the mid-1960s, when he moved here from his native Memphis. Along the way, he won the admiration of some formidable musical talents.

“I thought he was terrific,” said the revered Chicago singer-pianist Audrey Morris. “He was great at the personal part of it – expressing himself, and not sounding like someone else.”

Said vocalist-guitarist Frank D’Rone, “He knew how to get to people.”

Added cabaret performer Carla Gordon, who sang alongside Damon in recent years: “He had great chops, but his heart always led him.”

That about sums up the appeal of Damon, who owned a resplendent baritone and used it to considerable emotional effect. When Damon stepped into the spotlight, he did not hold back.

This tendency made him a tad overbearing early in his Chicago career, in the 1960s and ’70s, as Damon was quick to acknowledge.

“I was still learning how to be an entertainer, how to connect with an audience, how to put things together,” he told the Tribune in 1998. “In those days, I was the lounge lizard that was becoming Jimmy Damon.”

According to Damon and many others, comic actor Bill Murray caught Damon’s lounge-lizard act at the long-gone Cousins’ Club, on East Superior Street, when Murray still was honing his craft at Second City. Thus Murray found the inspiration for the unctuous lounge singer Murray later would famously spoof on “Saturday Night Live.”

Not that Damon minded.

“I wasn’t upset,” he said in the Tribune interview, winding up for the punch line. “I just wish he’d sent me a check. He owes me a lot of money.”

That a child-prodigy country singer from Memphis would eventually become the quintessential big-city crooner defies the imagination, but show business careers sometimes unfold in unexpected ways.

Damon had gotten off to a quick start back home in Tennessee, singing as young Jimmy Demopoulos at Kiwanis Clubs and church functions. Elvis Presley and Johnny Cash would frequent the family’s diner, the New York Café, and young Demopoulos was smitten.

“At night we’d often go to hear singers who worked for my father (at the diner) during the day,” Damon said in the 1998 Tribune interview. “We’d listen to country. We’d go to Beale Street and listen to black music – blues, jazz. That’s where the action was.”

By the time he was a teenager, he was playing on a bill with Presley and Conway Twitty, recording for Phillips and Sun Records, appearing on Arthur Godfrey’s television show and basking in the adulation of a fan club devoted to him. After a stint in the Army, he decided he needed to push beyond country music, and “the only way to do that was to go up north,” he said.

So he headed to Milwaukee and then Chicago, renaming himself Jimmy Damon and by 1968 appearing on “Don McNeill’s Breakfast Club” radio show and regularly at Mister Kelly’s, the Playboy Club, the Empire Room at the Palmer House and other landmark spots.

The 1970s and ’80s were Damon’s heyday, and he hardly could keep up with demands for his art. But by the ’90s most of the old showrooms had disappeared, and Damon had to seek out opportunities in a shrinking environment for his brand of crooning.

“There’s not always a paycheck on Fridays in this business,” Damon told the Tribune in 2011, on the eve of being honored at the annual gala of Chicago Cabaret Professionals, at Park West.

“There have been ups and downs. …

“I only sing for a living – I don’t have (another) job. This is a total commitment.”

You felt that whenever Damon sang. Though he obviously owed an artistic debt to Frank Sinatra, whose music he featured in a Park West tribute in 1995 and elsewhere thereafter, Damon did this music his way. He consistently found his own tempos, dramatic peaks and nuances in Sinatra’s repertoire.

If you weren’t around when Sinatra was king, Damon kept that era alive.

“For those people who were younger and weren’t here for the magic of Mister Kelly’s, the magic of Palmer House, he wanted to let you know: This was fun, these were the great guys,” said music presenter Tracy. “And he wanted to share that with you.”

Even after all those decades, he somehow never lost his ardor for it.

“He always reflected this boyish enthusiasm for the music that was his passion,” said veteran music publicist Debbie Silverman Krolik in an email. “He was a Southern gentleman who made Chicago his home and always was so generous to this city with his musical gift.”

Though Chicago does owe Damon a great deal, the singer felt the debt ran the other way.

“Musically, it’s been a great place for me to learn how to sing,” Damon said in the 2011 Tribune interview.

“What I learned here was how to separate myself from the rest of the acts – how to be Jimmy Damon, not some other creep.”

In addition to his wife, Damon is survived by his daughter, Dana Damon-Trentadue (and her husband Bartolomeo Trentadue); a grandson, Antonio Trentadue; and another daughter, Alexa Damon-Soegaard (and husband Juan Soegaard).